OBSTETRICAL ULTRASOUND EXAMINATION 2 nd /3 rd TRIMESTER

Transcription

1 OBSTETRICAL ULTRASOUND EXAMINATION 2 nd /3 rd TRIMESTER POLICY: Obstetrical ultrasound will be performed with an order from a physician or other qualified clinical practitioner. The examination will be supervised and interpreted by a radiologist or other licensed practitioner who is qualified by reason of training to recognize normal and abnormal maternal and fetal anatomy, understand the pathophysiology of pregnancy, and integrate the patient s clinical circumstances and ultrasound findings to optimize the probability of accurate diagnosis. PURPOSE: To assess the status of a pregnancy in the 2nd and 3rd trimester and document normal and abnormal findings. INDICATIONS: Obstetrical ultrasound is indicated in some circumstances for uncomplicated 2nd and 3rd trimester pregnancies (e.g. estimation of gestational age, measurement of fetal growth, suspected multiple gestations, determination of fetal position) or for pregnancy complications (e.g. small- or large-for-dates, vaginal bleeding, suspected fetal death, premature rupture of membranes, or preterm labor). Known or suspected fetal abnormalities (e.g. abnormal maternal serum screening, family history of congenital anomaly, advanced maternal age, abnormal fetal movement, or adjunct to amniocentesis) are appropriate indications for 2nd and 3rd trimester obstetric ultrasound, as are maternal conditions (e.g. abdominal or pelvic pain, pelvic mass, known or suspected cervical insufficiency, diabetes, hypertension, or teratogen exposure). This list of indications is not comprehensive and the decision to perform prenatal ultrasound is best determined by the primary obstetric practitioner. PATIENT PREPARATION: There is no special preparation for this examination. Patients should be instructed to take prescribed oral or injectable medication on their normal schedule. PROCEDURE: With infrequent exceptions (noted below), the examination will be performed from a transabdominal approach. For every image that includes measurements, excluding biometry images, an identical image should be captured with calipers removed. The elements of the examination are defined by the AIUM Practice Guidelines for the Performance of Obstetric Ultrasound (effective 10/1/2007). The elements and order of imaging for the complete examination are listed below, with the minimal number of images in parenthesis. 1

2 Panoramic examination (11 images) Maternal uterus and cervix Maternal adnexa/ovaries Fetal position Placental position Fetal Biometry (8 images) Biparietal diameter Head circumference Abdomen circumference Femur length Estimation of fetal weight Fetal Anatomy (30 images, 2 cines) Head Face (1 image, 1 cine) Brain Spine Heart (5 images, 1 cine) Stomach Kidneys Bladder Umbilical cord vessels and insertion sites Extremities Fetal biometry will be recorded on off-line computerized obstetric reporting software (e.g.: Viewpoint) to calculate estimates of gestational age and weight. When available, computerized obstetric reporting software (e.g.: Viewpoint) should be used to report fetal anatomy, maternal structures, and any abnormalities identified. PANORAMIC VIEW Panoramic images are intended to demonstrate the uterine contour, uterine abnormalities (e.g. duplication anomalies, fibroids), fetal position, situs, the placenta and its relationship to the cervix, and amniotic fluid volume. The ovaries/adnexa are also routinely evaluated for abnormalities. Minimal stored images should include: Three long axis views of the uterus (sagittal midline, right and left parasagittal) labeled Long Rt, Long ML, and Long LT. One image should be optimized to display the fundus and one image optimized to demonstrate the position of the placenta relative to the internal cervical os Two long axis views of the cervix labeled Long Cervix, to demonstrate the entire endocervical canal, internal and external cervical os and 2

3 position of the placenta (if visible in the lower uterine segment) relative to the cervix. These images must be obtained without excessive bladder filling or uterine contractions. The fetus must be displaced from the lower uterine segment to allow amniotic fluid to oppose the internal os. The cervix will be measured from the internal os to the external os on one image. In circumstances where imaging of the cervix is critical (e.g. history of incompetent cervix, preterm labor, previous cervical procedures/surgeries), a careful endovaginal examination will be performed Three transverse views of the uterus labeled Trans Sup, Trans Mid, and Trans Inf, to demonstrate the lateral uterine walls, fetal position and placental position Long and short axis images of each ovary should be obtained and labeled Long Rt/Lt Ovary and Trans Rt/Lt Ovary as appropriate. If visualization of the ovaries is adequate, three orthogonal dimensions should be measured. If the ovaries are not reliably visualized, representative long and short axis images of the adnexa should be obtained and labeled Long Rt/Lt Adnexa and Trans Rt/Lt Adnexa as appropriate In pregnancies at or beyond 25 weeks, the amniotic fluid index will be documented. A focused image of each quadrant of the uterus will be obtained, in either longitudinal or transverse planes, to include the largest vertical pocket of amniotic fluid and labeled RUQ, LUQ, RLQ, or LLQ, as appropriate. The amniotic fluid pocket in each quadrant will be measured to exclude the umbilical cord (color Doppler should be utilized to improve visualization of the cord) and fetal parts, and added to the measured pocket in each of the other quadrants to arrive at the amniotic fluid index. Measured pockets of fluid should be at least 1cm in width. Quadrants without perceptible amniotic fluid will be imaged and labeled; FETAL BIOMETRY Specified fetal structures will be imaged and measured to generate a composite or average estimate of gestational age. Multiple images and measurements of all structures will be obtained, and the sonographer will select the best measurement of each structure for inclusion in the composite or average age. The measured value of each structure will be recorded in the computerized obstetric reporting software to generate the estimate of gestational age and fetal weight. Structures that cannot be reliably imaged and measured will be excluded from the composite or average gestational age calculation. Minimal stored images shall include: Two images of the biparietal diameter (BPD) obtained from a lateral (parietal) approach in a transverse plane that includes the thalami and 3

4 cavum septi pellucidi. The BDP will be measured at the widest point of the skull from the outer table of the calvarium closest to the transducer to the inner table of the calvarium furthest from the transducer. Two images of the head circumference (HC) obtained at the same level of the fetal head as used for measurement of the BPD. The HC will be measured in two dimensions at the outer table of the calvarium to include the longest (occipitofrontal) and orthogonal diameters, or with the ellipse tool available on the ultrasound machine; Two images of the abdominal circumference (AC) obtained in a transverse plane of the abdomen to include the junction of the portal sinus and intraabdominal umbilical vein. The AC will be measured at the skin surface in two dimensions to include the longest and orthogonal diameters, or with the ellipse tool available on the ultrasound machine; Two images of the femur nearest the transducer oriented such that its long axis is perpendicular to the ultrasound beam. (If the near field femur cannot be reliably imaged, the opposite femur can be used for measurement.) The femur measurement will include the longest calcified (diaphyseal) dimension, excluding any specular reflection of the distal epiphysis. FETAL ANATOMY All complete 2 nd and 3 rd trimester obstetric ultrasound examinations will include a screening survey of fetal anatomy to identify normal structures and demonstrate common fetal malformations. It is not the intention of the screening anatomic survey to identify all fetal structures and/or malformations, nor characterize in any detail malformations that may be encountered. All structures included in these minimal requirements (detailed below) will be classified as 1) adequately visualized and within normal limits (WNL), 2) adequately visualized and abnormal, 3) not well visualized, or 4) not examined. Normal fetal structures that are not included in the minimal requirements can be imaged if encountered during the course of a standard examination. All abnormal fetal structures identified by the sonographer, whether required or not, shall be imaged. Minimal stored images shall include: Head: Images of the fetal head shall demonstrate the calvarium, its echogenicity, and contour. The frontal, parietal, and occipital segments shall be included; the crown may not be imaged because of fetal position. Images of the BPD, HC, and intracranial structures that also adequately demonstrate the calvarium are sufficient for documentation of the fetal head; Face: Documentation of the fetal face will include at least one coronal (tangential) view of the nose and upper lip and a cine clip in the same plane from anterior to posterior. The image(s) and cine shall be 4

5 labeled Nose/Lips. A profile view of the fetal face may be obtained but is not required. Profile views captured must demonstrate a fetal nasal bone (if present) and fetal chin contour. Profile views that are slightly off the sagittal midline may artifactually create the appearance of micrognathia, absent/shortened nasal bone, or other problems; Brain: Images of the fetal brain shall include at least one image of the midline falx and cavum septi pellucidi (images of the BPD and HC that adequately demonstrate the falx and cavum septi pellucidi are satisfactory for documentation.) At least two images will be recorded from the lateral (parietal) approach to include the lateral ventricle, ventricular atrium, and occipital horn and labeled Ventricle. The ventricular atrium will be measured in one image at the posterior margin of the choroid plexus, perpendicular to the long axis of the ventricle, from its medial to lateral walls. At least two images of the posterior fossa from a lateral (parietal) approach will include the cerebellum at its widest transverse diameter and the cisterna magna and labeled Posterior Fossa, Cisterna Magna or Cerebellum as appropriate. The transverse cerebellar diameter and cisterna magna can be measured in one image, but measurements are not required; Spine: The cervical, thoracic, lumbar and sacral segments of the fetal spine shall be imaged in long and transverse planes. The spine should be imaged when it is exposed to the examining transducer without intervening fetal tissues (i.e. fetal prone position) and when amniotic fluid is interposed between the fetus and uterine wall to optimize visualization of the fetal skin. Long axis view should be obtained to image as much of the complete length of the spine as possible and labeled Long spine. Representative transverse images of the cervical, thoracic, lumbar, and sacral segments shall be obtained and labeled Trans Spine C, T, L or S, as appropriate; Heart: Examination of the fetal heart will include at least one m-mode image of the heart rhythm and rate. At least one view of the four chambers shall be included and labeled 4 Chamber Heart. An image should be included that demonstrates the orientation of the fetal heart and position within the fetal thorax. Images of the heart can be obtained from the apical or lateral projection and should be magnified to occupy at least ½ of the field of view. The 4 chamber view must demonstrate symmetry of the ventricular chambers and symmetry of the atrial chambers. The ventricular and atrial septa and crux will be included. The moderator band should be visible in the right ventricle and the septum primum (flap of the foramen ovale) in the left atrium. A long axis image of each ventricular outflow tract should also be obtained and labeled LVOT or RVOT, as appropriate. A 3-vessel view should also be captured and labeled 3 Vessel View; consisting of the long axis pulmonary artery/ductus arteriosus, short axis ascending aorta and short axis superior vena cava. A transverse cine sweep from the upper abdomen (to include the stomach) through the great 5

6 vessels should be included in each examination, demonstrating the 4- Chamber View, LVOT, RVOT/3-Vessel View. When visualized in the course of a normal examination, the aortic and ductal arches may also be imaged and labeled Ao Arch or Ductal Arch as appropriate. Stomach: At least one transverse view of the upper fetal abdomen will include the stomach and be labeled Stomach. Kidneys: At least one transverse image of the fetal kidneys will be recorded to include the renal pelvis on each side labeled Kidneys. The kidneys should be imaged when they are exposed to the examining transducer without intervening fetal tissues (i.e. fetal prone position.) Images of the fetal spine that adequately demonstrate both kidneys are satisfactory for documentation. If dilated, the renal pelves should be measured in their maximal anteroposterior intrarenal diameter. Bladder: At least one transverse image of the urinary bladder will be recorded and labeled Bladder. Umbilical cord vessels and insertion: A transverse color Doppler image of the intrapelvic umbilical arteries (adjacent to the fetal urinary bladder) should be obtained. If this is not well seen, a cross-sectional image of the umbilical cord demonstrating the umbilical arteries and vein can be obtained instead. Any images demonstrating two umbilical arteries should be labeled 3 Vessel Cord. At least one transverse image of the anterior abdominal wall at the umbilical cord insertion will be recorded and labeled Cord Insertion. The placental cord insertion should also be evaluated, and a representative image obtained. Extremities: Documentation of the extremities should demonstrate the presence of both arms and legs. Images of upper extremities will be labeled Rt/Lt Humerus, Radius/Ulna or Arm, as appropriate. Images of lower extremities will be labeled Rt/Lt Femur, Tib/Fib or Leg, as appropriate. Images of the lower legs should demonstrate the presence or absence of clubbed foot/feet. PATHOLOGIC CONDITIONS: When pathologic processes are detected during the course of the examination, extra images are necessary to characterize the abnormality. One or more cine clips should be obtained of any detected pathology. The following is a description of commonly encountered conditions that should be considered during the examination and the minimum additional stored images expected for each circumstance. The list is not intended to be comprehensive, and sonographers are expected to apply their knowledge of maternal and fetal anatomy to provide clear images of the abnormalities they encounter. Some conditions and structures may be best imaged from an endovaginal approach or require color and/or spectral Doppler for optimal characterization. 6

7 Placenta previa: Every 2 nd and 3 rd trimester screening obstetrical ultrasound will demonstrate the placental relationship to the cervix. Maternal factors that may predispose to placenta previa (age, parity, previous cesarean section, prior previa) and vaginal bleeding should be noted in the patient history. The cervix shall be imaged when the urinary bladder is empty or mildly distended and the presenting fetal part displaced from the lower uterine segment to permit unobstructed sagittal views of the inferior margin of the placenta and the cervix in a single image. Contractions of the lower uterine segment shall be allowed to relax prior to imaging. At least two sagittal images of the placenta/cervix shall be obtained and labeled long cervix. If the placenta is implanted over the internal os, images should document the relative volume of placenta on each side of the os (i.e. anterior and posterior.) If the placenta is implanted within 2 cm of the internal os (low lying), images should clearly demonstrate the inferior edge and internal os, and measurement of the distance between the two recorded on the image. If there is a venous sinus or cord vessels on or near the leading edge of the placenta, color Doppler images should be obtained to clearly demonstrate the position of the vessels relative to the internal os. When diagnostic images of the placenta/cervix cannot be obtained transabdominally (e.g. low position of the fetus, obese patient), transvaginal images shall be obtained. Preterm labor/incompetent cervix: Patients at risk for preterm labor (contracting, pelvic pain, premature rupture of membranes, history of preterm labor or delivery) or incompetent cervix (prior preterm delivery, prior cervical surgery) shall be imaged with an endovaginal transducer between 20 and 34 weeks. Contractions of the lower uterine segment shall be allowed to relax prior to imaging. At least two transvaginal sagittal images of the cervix will be obtained to include the internal and external cervical os, endocervical canal, and posterior lip of the cervix. Measurement will be recorded from the internal to external os and the images labeled long cervix. Patients with a cervical cerclage may be examined transabdominally if the images are diagnostic. Placental abruption: Patients at risk for placental abruption (vaginal bleeding, pelvic pain, labor, premature rupture of membranes, trauma) shall be examined with attention to the placental implantation. Specific evidence of subplacental or subchorionic hematoma shall be sought, documented, and labeled long right or left and transverse as appropriate. The umbilical cord insertion into the placenta shall be identified (if not obstructed by the fetus) and recorded. When a followup examination of placental abruption is requested, the sonographer shall review the original exam and attempt to reproduce similar imaging planes to allow comparison of the hematoma size. In pregnancies where a hematoma is documented and >26 weeks, umbilical artery spectral Doppler shall be obtained and recorded (3 separate images.) 7